Electrical measuring instrument.



forming a part of 35 this application.

CHARLES EDWIN FOSTER, OF ROCHESTER, NEW YORK.

ELECTRICAL MEASURING INSTRUMENT.

Specification of Letters Patent.

Pa-tented May 21, 1910.

Application filed February 24, 1908. Serial No. 417,255.

To all whom it may concern:

Beit known that I, CHARLES EDWIN Fos- 'I'ER, of Rochester, county of.Monroe, and State of New York, have invented certain 5 new and useful.-Improvements in Electric Measuring Instrun'ients; and l do herebydcclare the following to be a full, clear, and exact description of thesame, reference being had to the accompairving drawings,

this specification, and to the referencelctters marked thereon.

'The presentinvention relates to electrical instruments of the thermalmeasuring type, or more particularly those in which the quantities to bemeasured cause a part to become longer and shorter under the action ofheat, and it has for an object to secure eonstance in the value ofthe-readings of the instrumentand the elimination of errors due to thechange in the condition of the heat affected portion.

' To this and other ends the invention con sists in certainin'iprovements and combinations of parts all will be hereinafter morethe novel "features being pointed out in the claims at the end of thespecification. I

In the drawings: Figure 1 is a diagrammatic View of an indicatingcurrent met r to which my invention hasd een adapted; and

Fig. 2 is a detail view of the thermal or heat affected portion. 1

The invention although embodied in an indicating current meter is notlimited to As shown, it comprises a thermal member A consistingpreferably of a fine Wire of some metal which does not easily oxidizeandwhich has a large temperature coeflicient of expansion. At the ends40 of the theri'nal member are arranged the bending members whichpreferably comprise broad, thin strips B and C formed, it

desirable, by rolling wire of relatively large cross section therebyoflermg less resistance to the current than the thermal member, so

. that the passage through them of the current does not materiallyaltect them. They are disposed so that they otter the leastpossibleresistance to the resultant bending when the -wire A becomes longer "orshorter. By this construction, those portions of the instrument whichare subjected to bending or twisting stresses are not appreciably heatedby the, electrical quantities to be measured or recorded andconversely'those portions of the instrument which are heated by theelecl t t l l l 'mal member of a trical quantity to be measured are notsubjected to bending or twisting stresses, thereby avoiding all errorswhich would be due to subjecting the thermal member to varying bendingstresses while it is being heated or cooled. Another thermal member E ispro vided as nearly as possible like member A in length cross sectionand material, and it; is com'iei-ted to bending members I) and F whichare constructed likcthe members B and- (1. The members 13 and F arefirmly secured to insulated supports Z) and f on the frame of theinstrument, while the members (I and l) are joined together at the point0. Also secured to both members C and D at the point e, is a tensionmember G, preferably embodying a helical spring secured to the frame bya hinge or otherwise at r so as to swing. This serves toretain themembers A and l) straight and under tension.

The thermal member I) with the bending members I) and F, acts as adevice for reducing the. action of the spring on the thermal member Athe latter becomes hotter. in other words, the force that keeps thethermal member A intension rapidly dilllllllSllCS as the temperature ofthe thcrn'ial member rises, so that the tension is at all times withinthe elastic limits of the thermal member, and when the thermal membercools it returns to its original length, thereby avoiding any errorswhich would result from the continued application in the therwhen it issubjected to an electrical overload and when it is consequently lessable to resist permanent distortion or stretching.

I t is preferable to employ some means of multiplying the elongation ofthe thermal member and for this purpose I may provide an indicatorcomprising preferably a dial M and a movable pointer or index J, havingsuitable connection with the thermal memher, In constructing thisconnection l may take advantage of the fact that the heat generated in awire is approximately proportional to the square of the electricalcurrent passing through it, thereby causing. the wire or thermal memberas it becomes hotter to sufi'er increasing increments of elongation forequal' or uniform increments of current. By taking advantage of thissquare law relation between thecurrent and the elongation, it ispossible to use a small ratio of multiplication of the. higher readingsof the instrument, and thus the tension in the tl1ertill mal member canbe made safely smaller when the thermal member is hotter and yet ai'nargin ot' torce will be left to overcome the friction of themeasuring or indicating between the thermal member and the indicatorcomprises a flexible connector H, preferably secured at one end to thethermal members at the point C, and having its other end secured to andpassed about an eccentrically mounted drum N, which moves the pointer Jabout pivot I. A spring K secured by a hinge or otherwise at lsmaintains a tension on the flexible connector ll, but. the force of thespring must not be so great that. the tension on thermal member E isrelaxed.

The action of the instrument is as follows: The current to be measured,or a known proportion of it, passes through the thermal member A and thebending members B and C, which are connected to the circuit by suitableleads 0), 7 of flexible form it desired Q in order to avoid hamperingthe movement of the mechanism. As the current does not pass through thethermal member E it causes a rise in temperature in the member A only,and consequently an elongation of the lat ter. Now A, with itstXltliHlUllS li and C,

forms one side of a triangle '1'), 1, 7', and since the base b, f isfixed in length and position and the side. 0 f does not alter in length,it follows that the apex 0 will swine in an arc'ot a circle whose centeris at Because the angle 6, c, f is an acute ingle, the morement of thepoint 0 will be approximately the direction of connector ii. and thesprint, K will cause a rotation of the drum N with a consequent. motionof the pointer orcr the scale ll. As the currentpassing through Aincreases, the movement of the mechanism proceeds until a position 1-has been assumed, its path of travel bein; approximately indicated bydotted lines Fig. 1. in this position it is evident. that the tensiondue to the spring (i is almost. wholly supported by the thermal member Eand there will be but little tension on member A. in fact, the movementmay be continued until there is no tension on A. beyond that. due to itsown weight. Cl'ianges in atmospheric temperature will all'ect bothmembers A. and

i equally and the resultant. motion of the point. c will be in such adirection as to produce no detectable dctlcctibn ot' the pointer .l imay cause two currents whose ditl'crcnce l desire to ascertain to passone through A. and the other through E in accordance with Fields method,and in this manner the instrument may be used as an indicatingwattmctcr.

What I claim is:

1. The combination with a pair of thermal members arran "ed at an angleto each other and connecte together, of a tension device acting on bothmembers at their point of connection and mounted to swing with saidpoint in a direction transverse to the direction of the pull of saidtension device, means for directing an electric current through one ofthe members and means for determining the transverse movement of i thepoint of connection.

The combination with a pair of thermal members arranged at an angle toeach other and connected together, of a tension device acting on bothmembers and secured at one end to swing and at its other end connectedto the thermal members at their point of connection, means for directingan electric current through one of said thermal members and means fordetermining the movement. of said point of connection.

The combination with a pair of thermal members arranged at an an le toeach other and connected together, of a tension device acting on bothmembers at their point of connection, an indicator, and a liexibleconnection between the indicator and he thermal members extemting fromtheir point oi connection in a direction trans 1 to the direction of thepull of the tension device.

4%. The combination with a thermal member, of apair of bending membersat the ends of the thermal member, having greater flexibility than thethermal member and ofl'ering less resistance to the passage of anelectric current, and means for directing an electric current throughthe bending meinhers and the thermal member.

5. The combination with a thermal meinber, of a pair of bending membersarranged at the end of the thermal member and each comprising a broadthin strip having greater flexibility than the thern'iai member, and.oli'ering less resistance to the passage of an electrical current, andmeans tor directing an elec ric currentt'hrough the bending members andthe thermal member.

6. The combination with a thermal member, of a bending member havinggreater flexibility than the thermal member and oll'ering lessresistance to the passage of an electric current, means l'or directing:an electric current through the thermal and the bending mei'nber, and anindicator orei ated by said thermal member.

7. The combination with a pair of thermal members, of bending n'ieinhersarranged at the ends of the thermal members. one bending member of onethermal men1her,being connected to a bending" member oi? the other I l lthermal member. a tension device connected to the connected bendingmembers, and an indicator connected to thesame bending members. 7

8. The combination with a pan of thermal the ends of the thermalmembers, one bendesenw 8 members, of bending members arranged at. I themovable member, 71 fiexible connection ing member of one thermal memberbeing ing n'lembers, and a tension device acting on connected to abending member of the other said drum. thermal member, a tension deviceconnected CHARLES BER-VIN FOSTER to the connected bending members, andan 1 Wit-tile ses:

indicator embodying a movable member an 1 WELL GRIFFITH,

eccentrically mounted drum connected to I BOLD H.

I be'hveen the drum and be connected bendin

